The Silver gene and it's effects on black and bay. Silver does not affect red pigment, so a chestnut horse that carries silver does not express the gene. They look like normal chestnut horses.
Part One: The Base Colors [link]
Part Two: The Cream Gene [link]
Part Three: The Champagne Gene [link]
Part Four: The Dun Gene [link]
Part Six: White Patterns [link]